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Kidney Week

Abstract: PO2187

Diffuse Background Monoclonal Light Chain Staining in Kidney Biopsies, Without Electron Dense Deposits: Is It Relevant?

Session Information

  • Onco-Nephrology - 1
    October 22, 2020 | Location: On-Demand
    Abstract Time: 10:00 AM - 12:00 PM

Category: Onco-Nephrology

  • 1500 Onco-Nephrology

Authors

  • Satoskar, Anjali A., The Ohio State University, Columbus, Ohio, United States
  • Al sanani, Ahlim, Marshall University, Huntington, West Virginia, United States
  • Brodsky, Sergey V., The Ohio State University, Columbus, Ohio, United States
  • Prosek, Jason, The Ohio State University, Columbus, Ohio, United States
  • Ayoub, Isabelle, The Ohio State University, Columbus, Ohio, United States
  • Nadasdy, Tibor, The Ohio State University, Columbus, Ohio, United States
Background

Pathologic diagnosis of monoclonal gammopathy (MIg)-associated kidney disease requires specific morphologic and immunofluorescence (IF) findings with deposits on electron microscopy. We have encountered kidney biopsies showing only diffuse “background” monoclonal light chain staining the renal parenchyma, without characteristic lesions of MIg-associated kidney disease or organized/non-organized deposits on ultrastructural examination. Such staining is either overlooked if weak, or can be over-diagnosed as MIg-associated kidney disease if strong, causing dilemma over the need for immediate clone-directed therapy. We performed a clinico-pathologic study to better understand its significance.

Methods

Database search over 12-year period revealed such 32 cases. Clinical and laboratory data was retrieved along with a mean follow-up of 13 months.

Results

Out of the 32 patients,15 (47%) had active myeloma by hematologic criteria (despite absence of myeloma casts on kidney biopsy) warranting immediate clone-directed therapy; but 11 (34%) did not have/develop myeloma-defining events till the end of follow-up period; 3 (9%) did not have detectable paraprotein; and 3 (9%) were lost to follow-up. The mean staining intensity of background monoclonal light chain was significantly higher in myeloma patients as compared to the non-myeloma patients (2.2 vs 1.5, p=0.03), but strong (2 or 3+) intensity of staining was seen in 36% (5/14) of the cases without active myeloma (Fig. 1).

Conclusion

It is important to recognize and document this isolated background monoclonal light chain staining in the biopsy report, but by itself, should not be classified as MIg-associated kidney disease. It does warrant a thorough hematologic work-up. It can help to unmask (previously unsuspected) underlying active myeloma which many patients. But it is important to note that there is a subset of patients that do not have active myeloma despite the strong background staining. Care must be taken to avoid inadvertant immediate clone-directed therapy in these patients, but periodic monitoring with hematologic and renal parameters to watch for possible malignant transformation is important.